Fiber reinforced resin molding is used extensively in a variety of fields including automobiles, housing facilities, and medical appliances as well as electric appliances due to its light-weight and high-rigidity features.
As for this fiber-reinforced resin molding, GFRP (Glass Fiber Reinforced Plastics) produced by molding using glass fiber as the reinforcing fiber and polypropylene, which is a type of thermoplastic resin, as the resin, and the like are well known.
The fiber-reinforced resin molding of this sort is used in the current automobile industry for main components of modules such as front-end module, door module and the like, torque converter bracket and intake system parts.
For example, as a method for manufacturing these fibrous resin moldings, injection molding and hollow molding are known which are used for manufacturing of these moldings by molding propylene homopolymer, low-density polyethylene and polypropylene composition containing glass fiber as the reinforcing fiber and talc (see for example Japanese Patent Application Laid-open No. Hei 9-328586).
The composition is molded at a die temperature higher than 100° C. to produce a resin molding with high-rigidity and uniform wall thickness.
However, when a fiber-reinforced resin molding is manufactured by the conventional molding method, lifting of the reinforcing fiber or protrusion of weld area may easily appear on the molding surface. This is not desirable from appearance viewpoints and poses a problem of lack of good design features.
Conventionally a few attempts have been made for solving the problem, such as film pasting on the surface of the resin molding or multiplayer containing no fibrous layer. However, these methods are not effective from industrial viewpoints. Although an alternative to reduce amount of the reinforcing fiber to be added is proposed, with this method, improvement of physical properties of the fiber-reinforced resin molding is not possible.
Due to the reasons as described above, conventional fiber-reinforced resin moldings were used mostly at such portion where appearance quality was not considered to raise a significant problem.